Thus far,only a handful of broadly reactive human neutralizing monoclonal antibodies (nmAbs) have been described, all of which were derived from HIV clade B-infected individuals. The overall goal of Project 2 is to exploit the broadly reactive neutralizing antibody (nAb) responses we have observed in some of the experimental monkeys infected with and/or vaccinated against simian-human immunodeficiency virus (SHIV) strains that encode primary R5 env genes of pediatric HIV clade C isolates from Zambia. Under the current HIVRAD, which is under no-cost extension, we have identified monkey sera that not only neutralize homologous SHIV clade C and the corresponding parental HIV clade C, but also heterologous HIV clade C as well as non-related HIV clade B strains. The neutralizing activity was shown to be mediated by IgG in several animals. Our experimental rhesus monkeys with cross-reactive nAb responses represent a valuable esource, and this proposal seeks to further identify the nature of the anti-HIV clade C Env nAbs that have developed. We hypothesize that some nAbs in these sera recognize conserved structures within HIVEnv, and we thus seek to develop novel nmAbs and to identify novel mimotopes. The Specific Aims of this proposalare: 1. To isolate nmAbs from B cells collected from monkeys with IgG nAbs that block HIV infection with both HIV clade C and B isolates. 2. To characterize the epitope specificity of the new anti-HIV clade C nmAbs and to test whether they display autoreactivity. 3. To use the phage display technology in conjunction with a novel computer-based analysis, termed 3DEX, to identify conformational mimotopes that mimic the epitopes of the novel anti-HIV clade envelope mAbs. In a parallel, independent approach, the phage display/3DEX strategy will also be used directly with polyclonal nAbs from the monkeys. By dissecting the nature of the cross-clade nAbs, we may uncover new HIV Env targets and our strategy may thus have a high impact on the development of anti-HIV clade C vaccines that seek to induce nAb responses.